1. Field of Invention
This invention relates to a method of making a length of heat conduction pipe in a vacuum environment, especially to a method by which a length of heat conduction pipe is made from a semi-finished heat conduction pipe with squelching, cutting and sealing steps in a vacuum environment.
2. Prior Art
Conventionally, heat conduction pipe is manufactured in batch according to demand of customer. Due to the variation in length for each batch, it is almost impossible to carry out planned-production for finished pipes stock. Furthermore, the production efficiency of batch type production is low, which often fails to meet the delivery due to the time-consuming process, as well as difficulty in production control for automatic production process.
In the Taiwanese Patent No. 1250913, a manufacturing method for heat conduction pipe is disclosed by the applicant, aiming at solving the above-mentioned problem, as shown in FIG. 1, in which a certain stock quantity of semi-finished heat conduction pipe with extended length longer than ordinary requirement is prepared in advance, and said semi-finished heat conduction pipe stock is cut to required length according to the order of customer. Thereby, the disadvantage in traditional batch manufacturing of heat conduction pipe is improved. This manufacturing method includes at least following steps as below:                1. a preparation step—in which bare Cu pipe of fixed size are prepared.        2. a primary sealing step—in which one end of the bare Cu pipe is squelched and brazed.        3. a powder filling step—in which metal powder is filled into each Cu pipe at the other end after the insertion of a coaxial center pin into each Cu pipe.        4. a sintering step—in which each Cu pipe is heated so that the metal powder forms a porous layer in the inner wall of each Cu pipe, and the center pin is retreated thereafter.        5. an evacuation and liquid filling step—in which heat transfer medium is filled into the interior of each Cu pipe after evacuation in the interior of each Cu pipe.        6. a secondary sealing step—in which the other end of each Cu pipe is sealed and squelched so as to finish the semi-finished product.        7. a shrinking step—in which the diameter at certain fixed point of each semi-finished Cu pipe is shrunken so that the length from the sealed end to the shrunken point of Cu pipe, i.e., the total length meets customer's need.        8. a cutting and brazing step—in which the semi-finished Cu pipe is heated and cut at the shrunken point and then brazed to seal.        9. a shaping step—in which Cu pipe thus cut to fixed length is bent or flattened to required profile according to customer's need.        
The main features of the above publication, as shown in FIG. 2(2A˜2E), includes step 7, i.e., the shrinking step, and step 8, i.e., the cutting and brazing step. Specifically, the semi-finished heat conduction pipe (100′) is cut to suitable length according to customer's demand. Since sealability is the most important feature of a heat conduction pipe for good function, it is very important not to destroy the sealability during the cutting of the semi-finished heat conduction pipe (100′). Therefore, shrinking is firstly conducted at the portion (101) to be cut, then squelching and cutting is executed, so that vacuum within the pipe is better maintained. At present, these processes are almost conducted at atmosphere condition. Because the atmospheric pressure is far bigger than the pressure inside the pipe, it often happens that the vacuum within pipe is vanished away at the instant of breakage occurred during squelching and sealing process.
In order to solve this problem, traditionally the semi-finished heat conduction pipe (100′) is disposed vertically in length determination method. A heater device (110) is used to heat the bottom portion of the pipe to a predetermined temperature, then the squelching and cutting is carried out at the shrunken portion (101), by a squelching and cutting equipment (120), and then brazing is conducted at the cut portion. At last, Cu pipe thus cut to fixed length is bent or flattened to required profile according to customer's need. The purpose of heating conducted at the bottom portion of pipe by the heater device (110) is, on one hand, the residual gas remained during the evacuation and liquid filling process is expelled to the upper portion, i.e., the portion to be cut (100a), which can be removed during cutting. One the other hand, positive pressure is generated within the pipe by heating so as to avoid the vacuum from becoming ineffective caused by the infiltration of outside gas happened during squelching and cutting. Heating temperature, e.g. for water as working medium within pipe, generally is controlled at 100° C. such that the pressure in the pipe becomes positive, i.e., bigger than atmospheric pressure.
Although positive pressure generated in pipe by heating can prevent the vacuum from becoming ineffective during execution of the method of length determination, however, the persons skilled in the art should understand that it is difficult to control precisely the heating temperature in view of the variation in property of each pipe. In addition, working medium more or less suffers vapor leakage during breakage happened in squelching and cutting step due to the fact that saturated vapor is filled within the heat conduction pipe, when the pipe is heated to 100° C. The leakage quantity is closely linked with the step of breakage, besides, it is deeply concerned with the temperature of heat conduction pipe. In other words, the higher the temperature of heat conduction pipe is, the bigger the leakage quantity becomes. For example, the saturated vapor pressure of water at 100° C. is 1.0 kg/cm2, while at 110° C. is 1.46 kg/cm2, the difference of saturated vapor pressure between these two temperatures is 46% at 10° C. difference in temperature. Therefore, the working medium charge quantity often suffers inconformity, even in each heat conduction pipe of the same production batch, which is usually the main factor of quality uncertainty in each production batch.